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Old 11th Aug 2017, 4:45 pm   #1
RojDW48
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Default Mystery home made loudspeakers

An interesting pair I picked up at auction. Beautifully put together but with a peculiar choice of drivers - ie, a Kef B139 and a Celestion T1295 (HF1300). That's right - nothing in the middle. The crossover is a work of art for a 2 way loudspeaker - I wonder if anyone recognizes it from maybe a hi-fi diy mag of the 60s?
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Old 11th Aug 2017, 6:20 pm   #2
Ted Kendall
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Default Re: Mystery home made loudspeakers

Radford Beaumonds, by the looks - you lucky - get that crossover!
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Old 11th Aug 2017, 7:10 pm   #3
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Default Re: Mystery home made loudspeakers

Well I'll be damned - so they are! Thank you Ted. And to think I popped them on top of my much loved Radford Studio 60s to test them and never guessed! There's a forum thread here - https://www.vintage-radio.net/forum/...757#post423757 - all about them. What an odd combination of drivers, but if the sainted Arthur thought they worked well together - it's odds on they did. These don't - one of the B139s is shot and the other sounds a bit wounded, but, having discovered they were designed by my hero, I shall seek out fresh B139s and give them a go. I hope later versions of the Kefs would work as well as I expect it will be difficult to find working examples of the originals.
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Old 11th Aug 2017, 9:25 pm   #4
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Default Re: Mystery home made loudspeakers

Well, I suppose the salient point is break-up in the B139, and being a solid piston it probably holds together well into the mid-range, although you'd want to roll it away quite quickly thereafter, hence perhaps the complex crossover.
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Old 11th Aug 2017, 11:22 pm   #5
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Default Re: Mystery home made loudspeakers

After a bit bit of judicious re-soldering and cleaning up I got one of them working properly and it was something of a revelation. No discernible lack of mid range at all. And they don't appear to have been kits (Radford were well known for providing kits and detailed instructions for cabinet building). The original labels - visible in the linked post above - had fallen off leaving an unshaded area on the back of each one. That was one very lucky auction find!
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Old 12th Aug 2017, 5:46 am   #6
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Default Re: Mystery home made loudspeakers

Nice find Roger. These lads will sell you a B139 - http://retrotechaudio.co.uk/kef_b139_bass_driver.html

Andy.
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Old 12th Aug 2017, 12:29 pm   #7
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Default Re: Mystery home made loudspeakers

Thanks Andy - I have found one for sale here in Bristol, which will hopefully replace the knackered one. The other actually appears to be OK now I have checked a few joints and cleaned up terminals. But that's a useful address to have anyway - thanks.
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Old 14th Aug 2017, 12:34 pm   #8
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Default Re: Mystery home made loudspeakers

One of KEF's own offering was a two way B139-T27 job, the Concorde ISTR.


I owned just the one in the early '70s. Driven initially by a homebrew 10W AD161-162 amp and later half a PW Texan. Never could afford a mate for it
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Old 14th Aug 2017, 5:26 pm   #9
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Default Re: Mystery home made loudspeakers

I think the Concorde was successor to the Duette (B139/T15). I remember hearing Concordes years ago and being impressed but I didn't know what drivers were inside. It seemed to me at first that the combination of that bass driver and a tweeter was bordering on perverse! But it certainly works.
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Old 14th Aug 2017, 6:22 pm   #10
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Default Re: Mystery home made loudspeakers

They did bring out the Concerto, with a B110 in the middle.

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Old 14th Aug 2017, 6:36 pm   #11
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Default Re: Mystery home made loudspeakers

Roger,

You might find that the B139s can be repaired. I had an pair that had been standing for some time and they sounded rough, as if the voice coil had been burned and was rubbing on the pole pieces. It turned out that the voice coil was indeed rubbing but it had not been overloaded or burned; the damp had got in and there was rust in the gap of the pole pieces causing the problem. The magnet assembly is very easy to take off, it's bolted onto the basket and the tolerance of the fit is loose because, having no dust cover over the front of the voice coil, the magnet is mounted after the cone is in position and centered by locating pins and the retaining bolts. It's well worth your time removing the magnet and checking everything out. If you find rust/muck/fluff in the gap then clean it out by forcing Blue Tak in there. The muck sticks nicely to the Blue Tak and leaves a clean gap when pulled out.

Nice speakers!

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Old 14th Aug 2017, 11:05 pm   #12
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Default Re: Mystery home made loudspeakers

A little bit of research suggests that your B139 units are the Mk2 Type 6171...

Steve.
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Old 14th Aug 2017, 11:48 pm   #13
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Default Re: Mystery home made loudspeakers

Thanks Steve - those look right. I have sourced a replacement for the dead one locally but I am greatly encouraged by your advice! I have never had the nerve to strip down a driver to its speech coil but in this case, there is really nothing to lose and I shall have a go.

Roger
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Old 15th Aug 2017, 10:36 am   #14
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Default Re: Mystery home made loudspeakers

That's the spirit!

I'm looking forward to reading how it goes - I have my fingers crossed for you. The ones I did are still fine some 20 years on

Don't forget to post some pics eh?

Cheers,
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Old 10th Sep 2017, 8:08 pm   #15
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Default Re: Mystery home made loudspeakers

I have just started to dismantle a B139 - bolts came out easily but the speech coil seems to be stuck inside somewhere - ie the magnet is trying to take the diaphragm with it! Rust maybe - or have I missed something?
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Old 11th Sep 2017, 6:18 am   #16
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Default Re: Mystery home made loudspeakers

Speech coil should come out of the magnet with no bother, sounds like it's seized inside. BTW, why are dismantling the driver, thought you were going to replace it? Autopsy maybe?

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Old 11th Sep 2017, 11:28 am   #17
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Default Re: Mystery home made loudspeakers

Hi Andy - I have replaced the dodgy (this) one in the Beaumonde and they both sound good now. In the light of Steve's advice I thought I might as well pull this driver apart to see if I can do anything with it. Looks like I'll need to get the Mem Sahib to support the cone while I give it a twist and yank! Nothing to lose really - it's no good as is.
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Old 12th Sep 2017, 6:42 am   #18
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Default Re: Mystery home made loudspeakers

Ahh, just curiosity, got you. Will it not budge with a bit of DC applied? It should shoot out. What in the name of Hades is stopping it? Curious indeed.

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Old 12th Sep 2017, 7:34 am   #19
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Default Re: Mystery home made loudspeakers

There are several possibilities. Rust in the gap formed around the voice coil or a melted voice coil former stuck to the pole piece...

David
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Old 12th Sep 2017, 10:40 am   #20
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Default Re: Mystery home made loudspeakers

Certainly was stuck and still is! Probably as David suggests - a bit of speech coil winding welded to the magnet! Hey ho - nothing lost and nothing gained. I might contact the lads Andy mentioned to see if they would like to recycle it.
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